1. Field of the invention
The present invention relates to a bidirectional printing device which may be advantageously employed as a printing means mounted for example on an electronic cash register (ECR) or the like.
2. Description of the Prior Art
Bidirectional printing devices for printing characters by moving the print head in one direction, then in the reverse direction thereof, i.e. bidirectionally, are used as printing means for electronic cash registers. With such printing devices, one line is printed as the print head is moved in one direction, and another line as it is moved in the reverse direction. That is, two lines are printed while the print head completes one bidirectional travel. When not performing printing operation, the print head is placed in a standby position where it stopped at the end of the preceding printing operation (i.e. at one end of the printing paper width). When printing operation is resumed, the print head starts to move toward the printing area on the printing paper. When the print head is detected as having reached one end of the printing area width, a reset signal described below is produced, in response to which the printing operation by the print head is started.
The reset signal is produced, for example, in response to a normal/reverse rotation instructing signal which instructs the rotating direction of a drive motor for driving the print head and the output signal from an optical detecting means which optically detects the print head positioning. The reset signal is classified into two kinds, one being the right reset signal which is given to start printing from the right end toward the left end of the printing area, and the other being the left reset signal which is given to start printing from the left end toward the right end of the printing area. Both right and left reset signals are used to determine the print start position and printing direction of the print head. In continuous printing operation, the right and left reset signals are alternately produced.
In such a bidirectional printing device, either right or left reset signal can be lost, for example, because of disconnection in a circuit within the printing device. In such a case, e.g., if the right reset signal is lost when printing should be made by moving the print head from the right end toward the left end of the printing area, the printing operation may, for example, be suspended without issuing notice to the operator, or erroneous printing may be made because of erroneous response to the subsequently given left reset signal.